Watch crystal



Nov. 26, 1940.

MORF WATCH CRYSTAL Filed Oct. 10, 1938 lNVENTOR PL V 0w A TTYS:

Patented Nov. 26, 1940 UNITED STATES PATENT OFFICE 3 Claims.

The present invention relates to watch crystals. Firstly the questionarises about the tightness of the joint between bezel and case band. Insocalled watertight watches the cooperation of the crystal edge with theborder of the bezel must be perfect on the whole circumference which isa very hard task especially in fancy watches for which already manyproposals have been made even for the most complicated forms. Thecrystal in general is feather edged and cooperates with a flange or anotch. The problem becomes complicated when a crystal has to be adjustedto a watch case the bottom of which cannot be opened. It should bepossible in such a case to withdraw the crystal from the outside withoutdamaging the watch.

The object of the present invention is a watch crystal particularly forwatertight watches having an immovable bottom. This watch crystal madeof an easily compressible material and elastic materialis characterizedin that its border is perpendicular to a plane tangent to the center ofthe crystal and comprises at least on a fraction of the border a notchor an elevated portion for removing it from its rest.

The annexed drawing represents as an example three embodiments of awatch crystal according to the invention.

Fig. 1 is a diametrical section of a first embodiment for a circularcrystal,

Fig. 2 is a diametrical section of a second embodiment for a circularcrystal,

Fig. 3 is a diametrical section of a third embodiment for a circularcrystal,

Fig. 4 shows a rectangular crystal by a section of which Fig. 5 is aplan view.

In the crystal according to Fig. 1 the edge a is constituted of theouter surface of a rim b perpendicular to a plane tangent to the centerof the crystal. This border is cylindrical and has a certain height andis intended to be introduced with a tight fit into the correspondingcylindrical upper portion 0 of a rest, for instance of a watch bezelmade in one piece with the bottom. Since the crystal is made of aslightly compressible and elastic material and its edge is perpendicularto a plane tangent to the center of the crystal it is easily understoodthat the compression stresses are the largest just parallel to saidplane and try to press the edge a with a maximum pressure against thewall 0 of the case. In order to have a hold on the crystal from theoutside and to be able to remove it when the necessity occurs the edge ais provided at its upper portion with a continuous ledge d constitutinga shutting rim projecting over the wall 0 of the rest.

In the crystal according to Fig. 2 the edge a is provided with aperipheral groove d which is also continous and is at the same levelwith 5 the upper edge of the wall 0 of the rest. This figure shows alsoan inner supporting member e which may be either the dial of the watchor a ring of suitable dimensions and may give a radial pressure to therim b by pressing on its inner wall so as to render perfect the jointbetween edge a and its rest. The inner face of the rim b has here arecess 1 securing the relative position of crystal and supporting membere.

The crystal according to the Fig. 3 is thickened on its border.

The Figs. 4 and 5 show also a crystal which is thickened on its border,but the crystal is here rectangular and the peripheral groove 01' ishere replaced by notches 01' arranged on both sides of the small axis ofthe crystal and made in the two small sides at the same level with theupper edge of the wall 0.

The crystal according to the invention is preferably made of a plastictransparent material slightly compressible and elastic. The syntheticresins of the acrylic and vinylique type are particularly suited forproducing such a material.

What I claim is:

l. The combination with a watch crystal adapted to fit an inner surfaceof the watch, having a slight curvature and made of a slightlycompressible and elastic material, a rim steeply arranged with regard toa plane tangent to the center of the crystal, a fitting surface beingprovided on said rim, said surface being adapted to be closely pressedagainst the correspondingly shaped inner surface of the watch, an innersupporting member fitted into said rim and adapted to produce a radialpressure on said rim. 0

2. The combination with a watch crystal adapted to fit an inner surfaceof the watch, having a slight curvature and made of a slightlycompressible and elastic material, a rim steeply arranged with regard toa plane tangent to the center of the crystal, a fitting surface beingprovided on said rim, said surface being adapted to be closely pressedagainst the correspondingly shaped inner surface of the watch, a recesson said rim, an inner supporting member fitted into said recess andadapted to produce a radial pressure on said rim.

3. The combination with a watch crystal adapted to fit an inner surfaceof the watch, having a slight curvature and made of a slightlycompressible and elastic material, a rim steeply and a recess on saidrim, an inner supporting arranged with regard to a plane tangent to themember fitted into said recess and kept in place center of the crystal,a fitting surface being proby said shoulder and adapted to produce aradial vided on said rim, said surface being adapted to pressure on saidrim.

closely pressed against the correspondingly ERNEST MORF. 5 shaped innersurface of the watch, a shoulder

